In recent years, from the viewpoint of effective use of energy, environmental preservation, and the like, a Rankine cycle type power generation system has been studied as a system for performing power generation using exhaust heat from ships, factories, gas turbines, and the like, terrestrial heat, solar heat, temperature difference between cooler deep and warmer shallow ocean waters, and the like as a heat source (for example, see Patent Literatures 1 to 3). In this case, when the above-described heat sources are used, a medium having a lower boiling point than water, for example, an organic fluid such as a fluorocarbon-based medium, is used as the medium. In this power generation system, as illustrated in FIG. 4, a medium is circulated through a circulation pump 6 within a cycle circuit 5 having a preheater 1, an evaporator 2, a turbine 3, and a condenser 4. Then, after recovering heat from the above-described heat source, the heat medium is pumped into the evaporator 2, heat exchange with the medium is performed, and the heat medium is evaporated and gasified. In addition, the heat medium passing through the evaporator 2 preheats the medium in the preheater 1 provided in a previous stage of the evaporator 2.
The gasified medium is expanded in the turbine 3 to rotate and drive the driving shaft 3a and drive the power generator 7. The medium expanded in the turbine 3 is condensed by the condenser 4 and circulated to the circulation pump 6.
When the power generator 7 is driven, an alternating current (AC) to be output is converted into a direct current (DC) by the rectifier 9. Further, the DC is reconverted into an AC by a system linking inverter 10 and the AC is externally output as generated power.
In an organic Rankine cycle type power generation system, a change amount in heat energy output from the heat source is large. Although it is only necessary to change the number of rotations of the power generator 7 in order to cope with the large change amount, it is necessary to consider the efficiency of the turbine 3 in a configuration in which the turbine 3 serves as a drive source of the power generator 7. It is preferable to operate the turbine 3 in a rotation region having high operation efficiency. Therefore, when the number of rotations of the turbine 3 and the power generator 7 is intended to be changed based on an output energy change of the heat source, a change width is limited.
Therefore, a technique for coping with a large output energy change of the heat source by providing a plurality of power generation units having the turbine 3 and the power generator 7 and changing the number of power generation units to be operated is also disclosed in Patent Literatures 1 to 3.